[vsnet-alert 1387] (fwd) Orbital Period of RX J0757.0+6306 (Thorstensen)

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

From owner-vsnet-adm@kusastro.kyoto-u.ac.jp Sat Dec 20 22:05 JST 1997
Date: Sat, 20 Dec 1997 08:05:03 -0500
From: "John R. Thorstensen" <thorsten@Dartmouth.EDU>
To: vsnet-adm@kusastro.kyoto-u.ac.jp
Reply-To: vsnet-adm@kusastro.kyoto-u.ac.jp
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Subject: Orbital period of RX J0757.0+6306
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Hello VSNetters,

Gaghik Tovmassian (UNAM) recently called attention to 
RX J0757.0+6306, for which he quoted a most likely orbital
period of 81 +- 5 minutes (vsnet-chat number 663).
The object has very strong H emission and he noted
the similarities with WZ Sge (another very short-period, 
strong-lined cataclysmic).  In addition the object 
showed 8.5-minute oscillations in its light curve on 
several occasions, suggesting the possibility of a DQ 
Her classification.

I obtained spectra of this remarkable object on 
December 18 and 19 UT, using the MDM 2.4-m telescope
and modular spectrograph, at 3 A FWHM resolution 
from 4000 to 7500 Angstroms.  The hydrogen lines are indeed
extremely strong, with H-alpha having an equivalent
width of about 200 Angstroms.  HeII 4686 is not unusually
strong, with an equivalent width of 13 A, about 1/10 the strength
of H-beta.  The strong H lines made it possible
to measure good radial velocities in this object, for
which I guesstimate a magnitude well fainter than 17 
(see Bob Fried's observations reported below).
Discarding a few weakly-exposed spectra taken 
through moonlit clouds left 67 exposures of 6
minutes each.  The spectra covered a 6.79 hour range
of hour angle.   

The radial velocities of the emission lines define
an unambiguous period 

	0.05982 +- 0.00013 days,

or
	86.14 +- 0.19 minutes.

The radial-velocity curve on this period is fairly 
clean (amplitude/scatter = 2.8).  While daily
cycle-count aliases are present in the periodogram,
they are weak and symmetrically distributed around
the main peak.  If the weather clears tonight, I may
be able to decrease the ncertainty slightly.

This period is at the upper end of Tovmassian's quoted range.

In addition, Joe Patterson (Columbia U.) passes on the following:

Robert Fried, Braeside Observatory, observed the star photometrically
for 7-hour runs on December 16 and 17.  The star was near magnitude
18, and no significant periodicity was seen (to a limit of 0.07
mag) near the range of a possible orbital period (1-4 hr).
However, a significant signal was detected at 515.1+-0.3 s, with
a full amplitude of 0.06 mag.


	John Thorstensen

	Department of Physics and Astronomy
	Dartmouth College

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